hrStorage Host Resources MIB Maximum Storage

Resolving The Problem

The hrStorage Host resources MIB (management information block) can only report 8TB of storage. Anything larger will show as a negative ( - ) number in a communications trace or at the SNMP (Simple Network Management Protocol) manager. This is due to the design specifications found in RFC 1514.

hrStorage returns the number of blocks of storage on the system. Each block is 4096 bytes. Per the RFC, the variable to hold this value is defined as an integer, meaning the maximum value it can hold is 2147483647.

2147483647 * 4096 = 8796093018112 bytes or exactly 8TB. When this RFC was created in 1993, 8TB of storage was unheard of.

Due to the value being too large for the variable, it appears to be a negative value. SNMP is working as designed.

**** UPDATE Dec 2014 *****
At R710 and higher, and with new function PTFs for R710 and R720 applied, CHGSNMPA now provides the ability to configure block sizes for both storage pools (hrStorageTable) and disk units (hrDiskStorageTable). The SNMP agent will now return size information for storage pools and disk units based on the values configured with CHGSNMPA. Note that *DFT for storage pools means that the system determines the block size used. For disk units *DFT means that a block size of 1024 is used.
The Block Size can be increased to a maximum of 32768 which means that returning the maximum number of blocks (2147483647) with a block size configured in CHGSNMPA of 32768 can now represent 64TB of storage for both storage pools and disk units.

If the block size is changed with CHGSNMPA, the SNMP server must be ended and restarted in order for the new block size to be used by the agent.

The following PTFs introduced this functionality:

R710 - SI55506 and SI55487

R720 - SI55539 and SI55537